In 1974, an uncontrolled case series was published describing children who allegedly developed mental retardation and epilepsy following receipt of the whole-cell pertussis vaccine. Over the next several years, fear of the pertussis vaccine generated by media coverage of this report caused a decrease in pertussis immunization rates in British children from 81% to 31%; the decrease in vaccine use resulted in >100,000 cases and over 600 deaths from pertussis. Decreased immunization rates and increased pertussis deaths also were seen in Japan, Sweden, and Wales.
The National Childhood Encephalopathy Study (NCES), conducted in the United Kingdom from 1976 to 1979, suggested the possibility of a relationship between the vaccine and encephalopathy, although methodologic problems with this study were quickly highlighted. For example, the study included only a small number of cases that had been exposed to the vaccine. The IOM independently analyzed the NCES data in 1991 and concluded that there was a rare but causal relationship with encephalopathy in the immediate postvaccination period, even though there was no evidence that permanent brain damage occurred. A reanalysis by the IOM in 1994 reached a different conclusion—wholecell pertussis vaccine did not cause encephalopathy
Other studies also refuted the initial findings of the NCES. For example, another UK study compared over 130,000 children who had received DTP with a similar number who had received only DT and found no association with encephalopathy. In Denmark, a shift to administration of pertussis vaccine earlier in life was not followed by a shift in diagnosis of neurological disorders. A study in Tennessee found 2 cases of encephalitis among 38,171 children who had received 107,154 DTP shots; in both cases, the onset of symptoms was >2 weeks following immunization. Finally, in a case-control study conducted in Washington and Oregon states involving 218,000 children, 424 cases with neurological illness were each matched with 2 controls. No association was seen with DTP administration, even when the analysis was restricted to encephalopathy or complicated seizures and adjusted for factors that might have affected vaccine administration.
In a study published in 2006, the records of four large US health maintenance organizations were used to address this issue once again. A total of 452 children with encephalopathy diagnosed between 1981 and 1995 were compared with matched controls without encephalopathy. Exposure to pertussis vaccine in any postvaccination time period was no more common among cases than controls. The maximum possible all-cause incidence of encephalopathy after pertussis immunization was 1 in 370,000, which is no different from the background rate of encephalopathy in young children.
The availability of new tools has shed light on the issue of pertussis vaccine and brain damage. In a landmark study, de novo mutations in the gene encoding a neuronal sodium channel protein were found in 11 of 14 patients who allegedly had suffered vaccine encephalopathy. These individuals were born with a molecular defect that would cause seizures and regression, vaccines or no vaccines. Despite this finding, and despite the fact that acellular pertussis vaccines have replaced whole-cell vaccines, encephalopathy remains an injury that can be compensated through the Vaccine Injury Table under the VICP.
—Marshall, Gary S. “Addressing Concerns About Vaccines.” The Vaccine Handbook: A Practical Guide for Clinicians. 3rd ed. New York: Professional Communications, Inc., 2010. 229-231. Print.